Temp Sensor

My FJ45 with temp sensor in the head has started reading high temps on the gauge. This came on suddenly, and my first thought was that it was sensor or gauge. When the engine is cold, the gauge no longer registers very low like it used to, and it appears that it is basically reading a quarter gauge higher than actual/normal. When I ground out the sensor lead, the gauge reads at the bottom of cold, like it should, and it goes to way high with no current a (key off) like it should, so I think the gauge is fine.

I know the sensor works via increasing resistance with increasing temperature (making the gauge rise with rising temps and rising resistance), so I assume that there is higher resistance in the sensor than normal (with odd vacillations occuring: when the engine is fully warmed up the gauge reads at the 3/4 mark, but will unpredictably sometimes rapidly jump up and down between 1/4 and 3/4 readings with varying engine speeds with and without actually driving the vehicle).

The sensor is only a couple of years old, though, so before I buy a new one, can anyone tell me how to test the sensor (manual doesn't give specifics) on my OLD style truck? OR can you think of another mechanism that might be occuring to cause these findings? Thnks!

Bad wire connections can increse the connections and this is a common problem on toyota gauges. As for testing, I just put an ohm meter on the sender and put it in a pan of water with a thermometer and warm it up.